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The Chd1 chromatin remodeler shifts hexasomes unidirectionally
Robert F Levendosky1, Anton Sabantsev2, Sebastian Deindl2
1T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, United States.
Elife
|December 30, 2016
Summary
Researchers created asymmetric hexasomes to study chromatin remodelers. They found that the Chd1 remodeler requires specific histone components for unidirectional sliding, influenced by modifications like ubiquitination.
Area of Science:
- Molecular Biology
- Chromatin Biology
- Biochemistry
Background:
- Nucleosomes, the basic units of DNA packaging, exhibit two-fold symmetry but are often asymmetric in vivo due to post-translational modifications (PTMs) and histone variants.
- Understanding nucleosome asymmetry is crucial for deciphering chromatin dynamics and gene regulation.
Purpose of the Study:
- To develop a method for generating precisely defined asymmetric nucleosomes (hexasomes) using the Widom 601 DNA sequence.
- To investigate the mechanism of chromatin remodeler Chd1, specifically its requirement for histone components and its sliding activity on asymmetric substrates.
- To explore the role of histone modifications, such as H2B ubiquitination, in modulating Chd1 activity.
Main Methods:
- Utilized the Widom 601 nucleosome positioning sequence to create oriented hexasomes.
- Employed biochemical assays to study the sliding activity of the Chd1 chromatin remodeler from *Saccharomyces cerevisiae* on these asymmetric hexasomes.
- Investigated the effect of H2A/H2B dimer presence and H2B ubiquitination on Chd1-mediated nucleosome sliding.
Main Results:
- Demonstrated that the Widom 601 sequence can generate hexasomes with defined orientation, serving as a tool for studying chromatin enzymes.
- Showed that Chd1 requires the H2A/H2B dimer on the entry side for efficient sliding, resulting in unidirectional hexasome translocation.
- Revealed that ubiquitin-conjugated H2B on the entry side enhances Chd1-mediated nucleosome sliding.
Conclusions:
- Asymmetric hexasomes provide a valuable platform for dissecting the mechanistic details of chromatin remodelers.
- Chd1 exhibits directional sliding activity dependent on the orientation of histone dimers and specific modifications.
- Nucleosome and hexasome asymmetry likely plays a significant role in chromatin organization and gene regulation in vivo.
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